Process and apparatus for removing sulfur from iron



Nov. 4, 1958 R. AN'roNsEN 2,859,105

PROCESS AND APPARATUS FOR REMOVING SULFUR FROM IRON original Fiied sept. 17. 1952 UnitedA StatesV Patent @Hice PROCESS AND APPARATUS FOR REMOVIN SULFUR FROM IRON Randolph Antonsen, Boston, Mass.

Original application September 17,A 1952, Serial No. 310,069. Divided and this application September 15, 1955, Serial No. 534,447

3 Claims. (Cl. 75-59) This invention comprises a new and improved process for removing sulfur from molten iron and simultaneously recovering the sulfur thus removed. It includeswithin its scope novel apparatus by which the process may be carried out.

The present application is a division of my copending application Ser. No. 310,069, tiled September 17, 1952, now abandoned.

The established practice of reducing iron ore to` metallic iron is to heat the ore in the presence of coke and lime in a 'blast furnace. Because both the ore and the coke usually contain large amounts of sulfur thisv element inevitably appears in the metal product. For many end uses the iron must be refined and this involves, among other things, the removal of sulfur. Were it not for the presence of sulfur many refining operations could be greatly shortened, notably in' the open hearth manufacture of steel in which considerable time is required to work out the sulfur, and incidentally carbon which must be replaced.

I have discovered that a large proportion of the sulfur content of iron can be easily removed therefrom and recovered as a valuable by-product by continuously treating a portion yof the slag while in the furnace and in contact with the surface of the molten iron to remove the available sulfur therefrom as by blowing Van oxygencontaining gas therethrough thereby reducing the sulfur content of the main slag body. The sulfur combined with the oxygen as oxides of sulfur is then removed from the treating zone and separated and recovered in accordance with known methods. Y

The principle according to which the process of my invention proceeds is as follows. ,It has long been known that the basic constituents of slags produced in blast furnace operations possess an' exceptional anity for sulfur. Were it not for this fact, substantially all of the sulfur which is normally present in the raw materials of the process would combine chemically with the molten mass of iron during the refining process. In operation, however, as the molten metal and slag collect in'. the hearth of the furnace, the greatest percentage of the sulfur of the system is concentrated in the slag. The sulfur content of the slag is usually quite substantial; in fact, it has been recognized that slags from blast furnace operation could constitute an implementing source of sulfur for the production of sulfuric acid.

Of course, the extent to which slag removes sulfur from the system is dependent upon the concentration of the sulfur in the iron and in the slag, upon the equilibrium of the sulfur between the iron and the slag, and upon the amount of iron and slag present in the system at any given time. As sulfur is being continuously removed frorn the slag, mass equilibrium is never reached and sulfur will continuously transfer to the slag from the iron mass until a new equilibrium-condition based upon the remaining relatively low sulfur contents of thel two materials is approached and the furnace is tapped. Sulfur transfer takes place both from the molten pool of iron on the hearth of the furnace and from the molten iron as it percolates through the slag.

An important feature of the process of my invention is that it is elective also for the removal of phosphorus from the molten iron. Since, during the slag-desulfurizing process, the slag tends to become more basic in nature it acquires a greater anity for the compounds of phosphorus, as well as the compounds of sulfur. The elimination of phosphorus from the molten iron is, of course, very desirable and accompanies the removal of sulfur. Further, by maintaining a highly basic slag as this treatment does it will be possible to reduce the amount of limestone needed in the charge; thus making for savings in limestone and coke per ton of product, reducing the back pressure required on the blast and increasing capacity.

Accordingly, it is the principal object of this invention to provide a process for .continuously removing sulfur from molten iron by reducing the sulfur content of the slag Within the furnace while maintaining contact of the molten iron with the slag so reduced in sulfur content.

Another object of the invention is to produce iron in a continuous process having a low sulfur content by a process carried on entirely Within the furnace and without requiring the addition of external heat.

These and other objects of this invention will be best appreciated and understood from the following description of an illustrative example of one way in which it may be advantageously put into practice taken in connection with the accompanying drawings in which,

Figure 1 is a view in vertical section of a blast furnace and auxiliary slag treater,

Figure 2 is an enlarged view, partly in elevation and partly in vertical section, of the slag treater, and

Figure 3 is a view in vertical section of the hearth portion of furnace equipped with integral peripheral treaters.

In the drawings is represented a typical blast furnace 10 provided with a stack section 12, a charging valve 14, a bosh 16, a gas withdrawal line 18 and a hearth or Crucible section 24, having a metal tapping hole 26 for withdrawing molten pig iron and a slag tapping hole (cinder notch) 28 for withdrawing liquid slag, all in aV conduit 32 being connected into the hearth section of the furnace above the normal level of the iron and below the normal top level of the slag. The upper conduit 34 is connected into the blast furnace above the normal top level of the slag. A trap 36 is provided in the upper conduit 34 to prevent blow back of gases from the furnace into the treater.

As shown in detail in Figure 2, the slag treater 30 consists of a metal shell 38 within which are a gas chamber 40, a bottom treating chamber 42 and a top chamber 44. Refractory door 46 supported on piers 4S separates the gas and treating chambers 40 and 42 respectively and contains a plurality of orifices 5l). Between chambers 42 and 44 is a refractory mass 52 supported on ring pier 54 through which pass a plurality of flues 56. These ues are preferably vertically aligned with orifices 50. A gas supply conduit 58 connects into gas Patented Nov. 4, 1958A,

chamber 40 and a'flue 60 is provided at the top of the treater.

In operation, when sufficient molten' iron and slag have accumulated so that slag flows into conduit 32, oxygen or an oxygen-containing gas, preferably preheated, is introduced into gas chamber 40 through conduit `53- and ows upward through minces-.50, 1through the slag in chamber 42 and through Iilues 56. As `soon as `enough slag has accumulated in the treatingI chamber 42 it will be lifted by theV gas stream through ues56 yinto upper chamber l44. The slag thus lifted by the gas streams into the upper chamber ows back into` the `blast furnace through conduit 34. During its ilow through the treater the slag is in contact with the oxygenrin thelifting gas for a time sufficient to enable-a substantial proportion of the sulfur in' the slagto combine withrthe oxygen to form oxides of sulfur which percolateA through and separate from the slag in theupper chamber and are-withdrawn from .treater30 through gas ue ,60. Y

So long as the reduction of iron ore is.-continued-and slag and iron accumulate inthe bottom ofthe blastfurnace the circulation of slag to treater 301is continued. The slag with greatly reduced sulfurcontent returning to the blast furnace through conduit 34`provides-aslag having a composition. reduced in sulfur, which as-I have stated above, attracts the sulfur causing equilibrium of the slag and the pig iron to change andv further causing a transfer of sulfur from the iron to the slag. The oxides of sulfur removed 'from treater 30 are recovered for further processing, for example, to produce sulfuric acid.

The apparatus shown in Figs. 1 and 2 is n'ot claimed herein but forms the subject matter of my'co-pending application, Ser. No. 659,727, led May-16,1957.

Various embodiments of apparatus inlwhichlthe-proc ess of my invention may be carried out will readilyA be apparent to those skilled in the art. One suchembodiment is illustrated in Figure 3. Instead of employing a separate treater as shown in Figure 2, a portion `of the blast furnace itself is used as a treating chamber. This consists of an annular recess 62, o'r al plurality of recesses separated by radial partitions from one another, built into the side wall of the blast furnace. Therecess is so constructed that it communicates with the ffurn'ace below the normal level of the slag pool-andl extends within the furnace wall above the toplevel of the slag thus providing a sealed marginal space above the surface of the slag therein separated from the-main body of the slag by overhanging depending wall 63 while maintained in direct contact therewith.

Passing through the outer wall of the blast furnace and into the bottom of the recess 62 and below the normal level of the slag pool is a plurality of gas ducts 64 through which oxygen or an oxygen-ContainingV gas is introduced for the same purpose as when treaterv 30 is used. At the top of the recess is a plurality of -gas outlet pipes 66 through which the oxides of sulfur and phosphorus are withdrawn.

In operation, when a suflicient marginal body of-slag has accumulated to seal the recess 62 the flow of oxygen or other oxygen-containing gas is commenced. The

gas passes through the marginal body of slag within and lbelow. the recess Vand out vent pipes-.66. carrying-o the sulfur oxides formed in the process. As the sulfur con` tent of the slag in the recess is reduced, there will be a phosphorus and the like impurities are to be removed have a body of slag in contact with its surface.

Having thus disclosed my invention and described in detail yan'illustrative..embodiment of it, I,claim as new anddesire to. secure by Letters Patent:

1. A processfor removing sulfur from themolten iron underlying alayer of ',slagin ablast furnace, which is characterized by the steps of forming a closed` recess. above a marginal portion of the slag layer in the furnace,

forcing an oxygen-containingV gas into the slag in said4 recess, and withdrawing sulfur oxides from the said re,-`

cess whiley theslag therein remains merged with the. slag layer in ythe furnace.

2. A process for removing sulfur vfrom the molten iron underlyingl a layer of slag in a furnace, which is characterized by the steps of segregating a minor marginal portion of the liquid slag layer from the main.

body ofthe slag in the furnace, maintainingfree liquid.V communication between the said two portions on all sides. of the main body, and continuously treating the segret gated portionwith oxygen-containing'gas to remove` s ulfur therefrom, thusk causing a migration of sulfur intothe segregated portion from the body portion of the sla layer.

3. A processfor removing sulfur from molten iron ullderlying a layer of molten slag ina blast furnace, which` is characterized by the steps of separating the layer of slag in'to amaininner body and a marginal body which surrounds and merges into the main body on all sides thereof, maintaining direct liquid communication and contact between the said bodies, and injecting oxygen'- containing gas into the marginal body thereby removing sulfur thereform,V causing migration of sulfur ontwardly,V

from the main body of the slag layer into themarginal body and thus from thevunderlying iron into the main body of the slag. Y

References Cited in the le of this patent UNITED STATES PATENTS 1,366,398 Lund Jan. 25, 1921 1,415,183 Lund May 9, 1922` 1,443,920 Levy Jan. 30, 1923 1,535,109 Davies Apr. 28, 1925 1,590,730 Evans .lune 29, 1926 1,646,728 Evans Oct. 28, 1927 1,753,891 Jones Apr. 8, 1930 It is merely necessary that the metal fromwhich sulfur, 

1. A PROCESS FOR REMOVING SULFUR FROM THE MOLTEN IRON UNDERLYING A LAYER OF SLAG IN A BLAST FURNACE, WHICH IS CHARACTERIZED BY THE STEPS OF FORMING A CLOSED RECESS ABOVE A MARGINAL PORTION OF THE SLAG LAYER IN THE FURNACE, FORCING AN OXYGEN-CONTAINING GAS INTO THE SLAG IN SAID RECESS, AND WITHDRAWING SULFUR OXIDES FROM THE SAID RECESS WHILE THE SLAG THEREIN REMAINS MERGED WITH THE SLAG LAYER IN THE FURNACE. 